Microstrip phase shifter having switchable path lengths

ABSTRACT

A microstrip phase shifter is inserted in a waveguide aperture, the phase shifting network consists of lightweight transmission line sections which can be switched by microwave diodes to provide the required phase shift. The diodes are switched in pairs, forward or back biased, so that the wave will traverse through a given path to complete the phase shifting according to the switched pair of the diodes.

United States Patent Robert A. Felsenheld Livingston, N .J.

Mar. 3, l 969 Mar. 2, 197 1 International Telephone and TelegraphCorporation Nutley, NJ.

inventor Appl. No. Filed Patented Assignee MICROSTRIP PHASE SHIFIERHAVING [56] References Cited UNITED STATES PATENTS 3,295,138 12/1966Nelson (333/31)UX 3,346,822 10/1967 Levy et a1. 333/31X PrimaryExaminer-Paul L. Gensler Attorneys-C. Cornell Remsen, Jr., Walter J.Baum, Percy P.

Lantzy, Philip M. Bolton, Isidore Togut and Charles L. Johnson, Jr.

ABSTRACT: A microstrip phase shifter is inserted in a waveguideaperture, the phase shifting network consists of lightweighttransmission line sections which can be switched by microwave diodes toprovide the required phase shift. The diodes are switched in pairs,forward or back biased, so that the wave will traverse through a givenpath to complete the phase shifting according to the switched pair ofthe diodes.

PATENT ED m 2 191:

sum 1 Dr 2 INVENTOR 120807 A. In SEN/1640 ATTORNEY PATENTEum 2mm sum 2.0? 2 r INVENTOR ATTORNEY Roamr renew/rew MICROSTRIP PHASE SHIFTIERHAVING SWITCIIAIBLE PATH LENGTHS BACKGROUND OF THE INVENTION In generalthis invention relates to microstrip phase shifters, and moreparticularly to transmissive-type phase shifters.

Transmissive phase shifters provide a fixed-length transmission linepath through the phase shifter which has active switching junctions atintervals along its length where additional line lengths may be added.The addition of one incremental length does not depend in any way uponthe addition of any length since the wave does not traverse unusedpaths. All phase shift increments are truly independent. A small numberof different increments having a binary relationship may be combined invarious ways to obtain many different values of phase shift in binarysteps. Transmissive phase shifters use fewer diodes, use them at lowerstresses, and require less closely held tolerances than tandemreflective-type phase shifters. Transmissive phase shifters also utilizediodes under conditions of good match during the steady state.

Since there is a need for improved transmissive phase shifters, there isprovided according to the invention a new twodiode per sectiontransmissive phase shifter as hereinafter described.

SUMMARY OF THE INVENTION It is an object of this invention to provide amicrostrip phase shifter.

It is another object of this invention to provide a two-diode persection transmissive phase shifter.

A feature of this invention is to provide a binary phase shiftingnetwork, the phase shifting network consisting of lightweight printedtransmission line sections which will be switched by microwave diodes toprovide to 360of phase shift, a typical phase shifting sectionconsisting of two diodes, one capacitor, and a biasing means.

A microstrip phase shifter is provided in a waveguide aperture, thephase shifting network consisting of lightweight printed transmissionline sections which are switched by microwave diodes to provide theproper phase shift; the diodes are shifted in pairs, forward orback-biased, whereby when the diodes are forward biased the waveprovides straight through fixed length paths and does not traverse anextra length of transmission line, and whereby when a reverse bias isapplied the wave will traverse the extra length of transmission line andprovide the proper phase shift through the network.

BRIEF DESCRIPTION OF THE-DRAWINGS The foregoing and the followingdetailed description will be better understood as reference is made tothe following drawings in which:

FIG. 1 shows a preferred embodiment of a two-diode per section s phaseshifter;

FIG. 2 illustrates a microstrip phase shifter positioned in a waveguideaperture;

FIG. 3 illustrates a typical array element microstrip phase shifterincorporating the features of the invention; and

FIG. 4 illustrates a binary phase shifter network utilizing theinvention which will provide 0 to 360 of phase shift in increments of22.5".

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, thereis shown a two diode junction phase shifter. Junctions A & B are aportion of a straightthrough fixed length path 11, 12. An extra lengthpath 13 of a transmission line in the form of a loop is added by properswitching of the diodes l4, 15. Both junctions A, B employ quarter wavesstubs 16, 17, and capacitors 18, 19 in the standard manner so thatbiasing voltages may be applied at 16 and the diodes operated in propersequence. The extra length path 13 is the phase shift in electricaldegrees and includes a matching taper section 20 coupling the signal tofixed length path 12.

IN this embodiment, both diodes 14, 15 are biased forward or backwardsimultaneously. When the diodes are forward biased by a bias voltageapplied to stub 16, the wave proceeds down the fixed length path ll, 12and does not traverse the loop 13, because an incrementalshort-circuited line section 21 which is added to halves of the loop CA& CB to form quarter wave lines EDCA and EDCB. This isolates these lineseven though they are conductively connected to the straight through lineat points A & B. Since points A & B are effectively equipotential andequiphase when diode 14 is conducting, the phase shift loop appears asan open circuit, and is isolated from the main line. The two-diode phaseshift section shown requires only one bias voltage, two diodes, and twocapacitors per phase shift section. This array is placed on aninsulating microstrip 22, the components may be integrated with thearray or placed at another position and coupled by appropriate leadsthrough a waveguide as shown in FIG. 2.

Referring now to FIG. 2, asection 23 of a waveguide containing amicrostrip phase shifter 24 is shown. The microstrip elements are heldin position within the rectangular guide by the retaining means 25(shown in dashed-lines) and terminal means 26 are added to the guide 23to provide suitable connections for the bias voltages and thecomponents.

The received energy, propagating within the rectangular waveguide, willcouple into a microstrip binary phase shifter through a printeddipole-to-microstrip transducer as shown in FIG. 3, wherein one side 24aforms the ground plane of the dipole, and the other side 24b forms thephase shifting array. The two sides 24 a, b of the microstrip form thedipole transducer so that the energy may be intercepted and phaseshifted according to the diodes switched in the array. The retainingmeans 25 may also serve as the shorting plane for the array.

A typical binary phase shifting network utilizing the concept of FIG. 1is placed on a microstrip board as shown in detail in FIG. 4. This phaseshift network consists of printed transmission line sections havingmicrowave diodes to provide 0 to 360 360phase shift in increments of22.5". This network provides four discrete phase shifts of 22.5, 45, 90,and 180 which can be added in any combination through switching of thediodes CR1 to CR8 to achieve the required phase shift. Each of the phaseshifting sections consists of two diodes i.e. CR,,CR two capacitors i.e.C ,C a bias quarter wave stub and a grounded quarter wave stub. Forexample when diode CR is forwarded biased to present a low impedance,energy will follow path AB. Conversely, when diode CR is reverse biasedto present high impedance, the RF energy will follow path ACE and a 180phase shift equal to the difference in path lengths will be obtained atpoint B. When diode CR8 is forward biased it is shunted by the loop ofpath ACB. Some of the energy will flow through this loop and cause ahigh standing wave ratio unless proper circuit compensation is provided.To reduce adverse effects on the transmission line, when diode CR, isconducting, a high impedance at points A & B is provided by anelectrical RF ground placed a quarter wave length one-quarter from bothpoints A & B.

Diode CR, placed between points C & D is biased in the forward directionto create quarter-wavelength paths ACD and BCD. With both diodes biasedin the forward direction, the phase shift section together with theswitched in line sections will appear appear as a high impedance atpoints A & B. The biasing network will not change the RF characteristicsof the phasing line. The bias for the diodes is supplied through quarterwavelength stubs, the capacitors are required to isolate the terminalsof the diodes from DC ground and provide an RF bypass. The completephase shift network of FIG. 4 consists of eight diodes and ninecapacitors. The effect of the insertion loss of these components on thecomplete phase network will be small because only five of the I?components are in series with an antenna at a given time. The basematerial (i.e. teflon fiberglass laminate, tellon) for the baseboardcircuit can keep this loss at a minimum.

By properly selecting the bias to each section, the phase shift throughthe array of FIG. 4 can be controlled in the illustrated increments.

Accordingly, there has been described a microstrip phase shifter whichis inserted in a waveguide aperture, the phase shifting networkcomprises printed transmission lines sections which are switched bymicrowave diodes to provide a desired phase shift. Diodes in aparticular section are switched in pairs, such that they are bothforward or back biased. When the diodes are forward biased, the waveproceeds straight through a fixed length path and does not transverse ashunted loop path since the section emulates quarter-wave lines. Whenthe diodes are reversed biased the waves will follow the longer shuntedpath to provide a corresponding electrical shift in degrees inaccordance with the length and shape of the path. A complete phase shiftnetwork is thus provided in this manner illustrated in FIGS. 1 through4.

Although I have described above a microstrip phase shifter which isdesigned to be inserted into a wave guide aperture, it should be clearlyunderstood that this novel type phase shifter is clearly suitable in anyphase shifting application.

I claim:

1. A phase shifter comprising:

first and second fixed length paths forming a first junction;

a shunting path across said first junction;

a quarter-wave stub coupled to each of said first and second fixedlength paths;

a first switchable device located at said first junction;

a second switchable device coupled between said shunting path and ashorting plane; and

means coupled for switching said first and second devices from one stateto another, said means including a source of bias voltage coupled to oneof said stubs, a first capacitor coupled to the bias voltage stub, and asecond capacitor located in said shunting path, whereby RF energy iscaused to follow a fixed length path or an extra length path formed bysaid shunting path.

2. A phase shifter according to claim 1 wherein said first and secondswitchable devices are diodes.

3. A phase shifter according to claim 2, wherein said bias voltageapplied to said bias stub causes said first and second diodes to besimultaneously forward or backbiased.

4. A phase shifter according to claim 3, wherein said bias stub iscoupled to said shorting plane by said first capacitor, and said stubconnected to said second fixed path is coupled directly to said shortingplane, whereby when said diodes are forward biased said phase shifteremulates quarter-wave lines.

5. A phase shifting array, each section of the array comprismg:

a first junction formed by first and second fixed length paths;

a shunting path across said first junction to provide the phase shift inelectrical degrees for each section;

a pair of quarter-wave stubs, each coupled to one of said first andsecond fixed length paths;

a first solid state device located at said firstjunction;

a second solid state device coupled between said shunting path and acommon shorting plane; and

means for switching said first and second devices from one biased stateto another, said means includes a source of bias voltage coupled to oneof said stubs, a first capacitor coupled to the bias voltage stub, and asecond capacitor positioned within said shunting path, whereby RF energyis caused to follow in response to said switching a fixed length path oran extra length path formed by said shunting path.

6. A phase shifting array according to claim 5 wherein said first andsecond solid-state devices are diodes.

7. A phase shifting array according to claim 6 wherein said bias voltageapplied to said bias stub causes said first and second diodes to besimultaneously forward or backbiased.

8. A phase shifting array according to claim 7 wherein said bias stub iscoupled to said common shorting plane b said first capacitor, and saidstub connected to said secon fixed path is directly coupled to saidcommon shorting plane, whereby when said diodes are forward biased thisphase shifting section emulates quarter-wave lines.

1. A phase shifter comprising: first and second fixed length pathsforming a first junction; a shunting path across said first junction; aquarter-wave stub coupled to each of said first and second fixed lengthpaths; a first switchable device located at said first junction; asecond switchable device coupled between said shunting path and ashorting plane; and means coupled for switching said first and seconddevices from one state to another, said means including a source of biasvoltage coupled to one of said stubs, a first capacitor coupled to thebias voltage stub, and a second capacitor located in said shunting path,whereby RF energy is caused to follow a fixed length path or an extralength path formed by said shunting path.
 2. A phase shifter accordingto claim 1 wherein said first and second switchable devices are diodes.3. A phase shifter according to claim 2, wherein said bias voltageapplied to said bias stub causes said first and second diodes to besimultaneously forward or backbiased.
 4. A phase shifter according toclaim 3, wherein said bias stub is coupled to said shorting plane bysaid first capacitor, and said stub connected to said second fixed pathis coupled directly to said shorting plane, whereby when said diodes areforward biased said phase shifter emulates quarter-wave lines.
 5. Aphase shifting array, each section of the array comprising: a firstjunction formed by first and second fixed length paths; a shunting pathacross said first junction to provide the phase shift in electricaldegrees for each section; a pair of quarter-wave stubs, each cOupled toone of said first and second fixed length paths; a first solid statedevice located at said first junction; a second solid state devicecoupled between said shunting path and a common shorting plane; andmeans for switching said first and second devices from one biased stateto another, said means includes a source of bias voltage coupled to oneof said stubs, a first capacitor coupled to the bias voltage stub, and asecond capacitor positioned within said shunting path, whereby RF energyis caused to follow in response to said switching a fixed length path oran extra length path formed by said shunting path.
 6. A phase shiftingarray according to claim 5 wherein said first and second solid-statedevices are diodes.
 7. A phase shifting array according to claim 6wherein said bias voltage applied to said bias stub causes said firstand second diodes to be simultaneously forward or backbiased.
 8. A phaseshifting array according to claim 7 wherein said bias stub is coupled tosaid common shorting plane by said first capacitor, and said stubconnected to said second fixed path is directly coupled to said commonshorting plane, whereby when said diodes are forward biased this phaseshifting section emulates quarter-wave lines.